Why does the LED (FlProg) not immediately go out?

Question

Arduino

Hello. The goal was to make a relay in the FlProg program, which will compare current and voltage and give a signal to turn off in the event of a short circuit. It is necessary that during short circuit the signal from the switch is still controlled. If the switch is open, then the signal to turn off was not given. Also, the shutdown signal stopped when the switch turned off. A wire is used as a switch, which can be disconnected by hand, and 13 pin (led) is used as an output (shutdown signal). The problem is this: When the wiring is disconnected (I turn off the switch), the LED does not go out immediately, but goes out slowly (smoothly)

How I connected the pins. Initially connected pins A0/A1(Analog) and 4(Digital) to 5V output.
When A1 is turned off (a voltage drop is simulated), the lamp lights up (signal to turn off the circuit breaker). Turning off the 4th input, we simulate turning off the switch and the lamp should go out immediately, but it does it slowly for some reason

Answer 1

Resistor from pin 4 to ground. Resistance - depending on the interference situation, from 1 to 100 kOhm.
PS Re-read the question "with other people's eyes." Is everything clear?